A conventional engine control device switches between homogeneous combustion and stratified charge combustion according to the engine load and engine rotation speed. For example, during the period from the beginning of engine cranking to a certain rise of the engine rotation speed, fuel is injected in the intake stroke such that homogeneous combustion is performed. During a normal operation after the engine is warmed up, stratified charge combustion, in which fuel economy is good, may be performed in a low load region, and high-output homogeneous combustion may be performed in medium and high load regions.
In Tokkai 2000-145510, published in 2000 by Japan Patent Office, when the temperature (water temperature, oil temperature) of the engine is equal to or less than a certain temperature during engine start-up, the air/fuel ratio is set to be lean such that the engine is operated by stratified charge combustion. In so doing, the exhaust gas temperature rises, promoting the activation of a catalyst inside an exhaust gas purification device, and hence the fuel economy is improved and hydrocarbons are reduced.